Our primary objective is to cultivate Treponema pallidum in vitro. All previous attempts to culture these organisms have been unsuccessful. These proposed studies differ from others in that tissue culture and aerobiosis will be employed. In order to obtain standard preparations of T. pallidum, it will be necessary to optimize the harvesting procedure to insure consistent yields of actively metabolizing organisms for the injected rabbit testes. It will then be important to prolong treponemal survival under defined in vitro conditions. This necessitates a characterization of the increased O2 sensitivity exhibited by the organisms in an in vitro environment. Insight into this area will enable us to minimize loss of treponemal viability, thereby facillitating successful cultivation. Attempts will be made to grow T. pallidum in the presence of various types of cultured cells. The accumulated knowledge concerning treponemal requirements in an in vitro environment will be applied to the formulation of a defined synthetic medium capable of supporting growth of the organisms.